How to use an attribute list an input to create filter expression in Custom Transformer

Hello,

Here is my situation. I have nearly 500 gdbs with exactly the same schema (each gdb contains 7 feature classes). I need to merge only two feature classes. My process also involves a loop and because I do not want to read all the gdb everytime, I have an index shapefile (one feature = one gdb extent) which I intersect with the area of interest in order to extract the names of the targeted gdbs.

Right now I have come down to creating a custom transformer which is able to select the good 2 features classes but in order for my filters to work, I need to be able to input the list of the previsouly selected gdb names in my epxression. So far this is what I manage to do.

I know there is something missing but I can't seem to figure out what. Basically, what I need is a way to feed the list of attributes to build the expression that will filter what I need.

Thank you for your help!